裂脑

Neuropsychologists study split-brain patients to investigate lateralization—the unique functions of the left and right brain hemispheres—and to understand communication between these regions. Since the corpus callosum, which normally transfers information between hemispheres, is surgically severed in these patients, researchers can assess each hemisphere's cognitive abilities independently and explore how brain regions interact.

The left hemisphere typically controls language and speech production, while the right hemisphere plays a large role in processing visuospatial information, such as judging spatial arrangements of objects. Information from one side of the body is processed in the opposite hemisphere, and each hemisphere contralaterally directs body movements on its opposite side.

Patients focus on a central cross symbol on a screen while images are presented to either the right or left visual field. Images in the right visual field are processed by the left hemisphere, while left visual field images reach the right hemisphere. Stimuli are shown for less than 150 milliseconds, preventing eye movement and ensuring only the tested hemisphere receives the information.

Split-brain patients cannot verbally identify objects presented to the left visual field because the right hemisphere, which processes that information, cannot generate language. However, they can draw these objects accurately with their left hand because the right hemisphere controls the left arm and processes the left visual field without needing communication from the speech-capable left hemisphere.

The corpus callosum is one of the largest nerve fiber bundles connecting the left and right brain hemispheres. It is surgically severed in patients with epilepsy to prevent uncontrollable neural activity from spreading throughout the entire brain. This inter-hemispheric disconnection allows researchers to study each hemisphere's independent functions.

The naming objects task measures the lateralization of verbal linguistic capability by presenting drawings to either the right or left visual field and recording whether patients can verbally identify each object. The dependent variable is the percentage of images shown in each visual field that patients accurately name, revealing which hemisphere controls speech production.

Research demonstrates that children experience fewer or less severe cognitive effects following corpus callosum severance compared to adults, suggesting young brains demonstrate greater plasticity. This finding has important implications for understanding how the timing of disconnection—whether during childhood or adulthood—affects cognitive recovery and adaptation in split-brain patients.